Copyright 2003 Scott/Jones Publishing Standard Version of Starting Out with C++, 4th Edition Chapter 7 Arrays

Chapter 7 slide 2 Topics 7.1 Arrays Hold Multiple Values 7.2 Accessing Array Elements 7.3 No Bounds Checking in C Array Initialization 7.5 Processing Array Contents 7.6 Using Parallel Arrays

Chapter 7 slide 3 Topics 7.7 Arrays as Function Arguments 7.8 Two-Dimensional Arrays 7.9 Arrays of Strings 7.10 Arrays with Three or More Dimensions 7.13 Introduction to the STL vector

Chapter 7 slide Arrays Hold Multiple Values Array: variable that can store multiple values of the same type Values are stored in adjacent memory locations Declared using [] operator: int tests[5];

Chapter 7 slide 5 Array - Memory Layout The definition: int tests[5]; allocates the following memory: first element second element third element fourth element fifth element

Chapter 7 slide 6 Array Terminology In the definition int tests[5]; int is the data type of the array elements tests is the name of the array 5, in [5], is the size declarator. It shows the number of elements in the array. The size of an array is (number of elements) * (size of each element)

Chapter 7 slide 7 Array Terminology The size of an array is: –the total number of bytes allocated for it – (number of elements) * (number of bytes for each element) Examples: int tests[5] is an array of 20 bytes, assuming 4 bytes for an int long double measures[10] is an array of 80 bytes, assuming 8 bytes for a long double

Chapter 7 slide 8 Size Declarators Named constants are commonly used as size declarators. const int SIZE = 5; int tests[SIZE]; This eases program maintenance when the size of the array needs to be changed.

Chapter 7 slide Accessing Array Elements Each array element has a subscript, used to access the element. Subscripts start at subscripts:

Chapter 7 slide 10 Accessing Array Elements Array elements can be used as regular variables: tests[0] = 79; cout << tests[0]; cin >> tests[1]; tests[4] = tests[0] + tests[1]; Arrays must be accessed via individual elements: cout << tests; // not legal

Chapter 7 slide 11 Accessing Array Contents Can access element with constant subscript: cout << tests[3] << endl; Can use integer expression as subscript: for (i = 0; i < SIZE;i++) cout << tests[i] << endl;

Chapter 7 slide 12 Global vs. Local Array Global array  all elements initialized to 0 Local array  all elements uninitialized by default

Chapter 7 slide No Bounds Checking in C++ C++ does not check if an array subscript is in the range of values for subscripts of the array Can access memory using subscripts that is before or after the memory for an array Can corrupt other memory locations, crash program, or lock up computer Not recommended

Chapter 7 slide Array Initialization Can be initialized during program execution with assignment statements: tests[0] = 79; tests[1] = 82; // etc. Can be initialized at array definition with an initialization list: const int SIZE = 5; int tests[SIZE] = {79,82,91,77,84}; Initialization list cannot exceed array size

Chapter 7 slide 15 Partial Array Initialization If array is initialized at definition with fewer initial values than the size declarator of the array, the remaining elements will be set to 0: const int SIZE = 5; int tests[SIZE] = {79, 82}; Initial values used in order; cannot skip over elements to initialize noncontiguous range

Chapter 7 slide 16 Implicit Array Sizing Can determine array size by the size of the initialization list: short quizzes[]={12,17,15,11}; Must use either array size declarator or initialization list at array definition

Chapter 7 slide 17 Initializing With a String Character array can be initialized by enclosing string in " ": const int SIZE = 6; char fName[SIZE] = "Henry"; Must leave room for \0 at end of array If initializing character-by-character, must add in \0 explicitly: char fName[6] = { 'H', 'e', 'n', 'r', 'y', '\0'};

Chapter 7 slide Processing Array Contents Array elements can be treated as ordinary variables of the same type as the array When using ++, -- operators, don’t confuse the element with the subscript: tests[i]++; // add 1 to tests[i] tests[i++]; // increment i, no // effect on tests

Chapter 7 slide 19 Array Assignment To copy one array to another, don’t try to assign one array to the other: newTests = tests; assign element-by-element: for (i = 0; i < ARRAY_SIZE; i++) newTests[i] = tests[i];

Chapter 7 slide 20 Display the Contents of an Array Can display character array by using its name: cout << fName << endl; For other types of arrays, must go element-by-element: for (i = 0; i < ARRAY_SIZE; i++) cout << tests[i] << endl;

Chapter 7 slide 21 Sum of Array Elements Use a simple loop to add together array elements: int tnum; double average, sum = 0; for(tnum = 0; tnum < SIZE; tnum++) sum += tests[tnum]; Once summed, can compute average: average = sum / SIZE;

Chapter 7 slide Using Parallel Arrays Parallel arrays: two or more arrays that contain related data Subscript is used to relate arrays: elements at same subscript are related Arrays may be of different types

Chapter 7 slide 23 Parallel Array Example const int SIZE = 5; // Array size string name[SIZE]; // student name double average[SIZE]; // course average char grade[SIZE]; // course grade... for(int i = 0; i < SIZE; i++) cout << "Student: " << name[i] << " average: " << average[i] << " grade: " << grade[i] << endl;

Chapter 7 slide Arrays as Function Arguments To pass an array to a function, just use the array name: showScores(tests); To define a function that takes an array parameter, use empty [] for array argument: void showScores(int []); // function prototype void showScores(int tests[]) // function header

Chapter 7 slide 25 Arrays as Function Arguments When passing an array to a function, it is common to pass array size so that function knows how many elements to process: showScores(tests, ARRAY_SIZE); Array size must also be reflected in prototype, header: void showScores(int [], int); // function prototype void showScores(int tests[], int size) // function header

Chapter 7 slide 26 Modifying Arrays in Functions Array names in functions are similar to reference variables – changes made to array in a function are reflected in actual array in calling function Need to exercise caution that array is not inadvertantly changed by a function

Chapter 7 slide Two-Dimensional Arrays Can define one array for multiple sets of data Like a table in a spreadsheet Use two size declarators in definition: const int ROWS = 4, COLS = 3; int exams[ROWS][COLS]; First declarator is number of rows; second is number of columns

Chapter 7 slide 28 Two-Dimensional Array Representation const int ROWS = 4, COLS = 3; int exams[ROWS][COLS]; Use two subscripts to access element: exams[2][2] = 86; exams[0][0]exams[0][1]exams[0][2] exams[1][0]exams[1][1]exams[1][2] exams[2][0]exams[2][1]exams[2][2] exams[3][0]exams[3][1]exams[3][2] columns rowsrows

Chapter 7 slide 29 Initialization at Definition Two-dimensional arrays are initialized row-by- row: const int ROWS = 2, COLS = 2; int exams[ROWS][COLS] = { {84, 78}, {92, 97} }; Can omit inner { }, some initial values in a row – array elements without initial values will be set to 0 or NULL

Chapter 7 slide 30 Two-Dimensional Array as Parameter, Argument Use array name as argument in function call: getExams(exams, 2); Use empty [] for row, size declarator for column in prototype, header: const int COLS = 2; // Prototype void getExams(int [][COLS], int); // Header void getExams(int exams[][COLS], int rows)

Chapter 7 slide Array of Strings Use a two-dimensional array of characters as an array of strings: const int NAMES = 3, SIZE = 10; char students[NAMES][SIZE] = { "Ann", "Bill", "Cindy" }; Each row contains one string Can use row subscript to reference the string: cout << students[i];

Chapter 7 slide Arrays with Three or More Dimensions Can define arrays with any number of dimensions: short rectSolid[2][3][5]; double timeGrid[3][4][3][4]; When used as parameter, specify all but 1 st dimension in prototype, heading: void getRectSolid(short [][3][5]);

Chapter 7 slide Introduction to the STL vector Defined in the Standard Template Library (Chapter 16) Can hold values of any type: vector scores; Automatically adds space as more is needed – no need to determine size at definition Can use [] to access elements

Chapter 7 slide 34 Declaring Vectors Vectors require vector header file Declare a vector: vector scores; Declare a vector with initial size 30: vector scores(30); Declare a vector and initialize all elements to 0: vector scores(30, 0); Declare a vector initialized to size and contents of another vector: vector finals(scores);

Chapter 7 slide 35 Growing a Vector’s Size Use size member function to determine size of a vector: howbig = scores.size(); Use push_back member function to add element to a full array or to an array that had no defined size: scores.push_back(75);

Chapter 7 slide 36 Removing Vector Elements Use pop_back member function to remove last element from vector: scores.pop_back(); To remove all contents of vector, use clear member function: scores.clear(); To determine if vector is empty, use empty member function: while (!scores.empty())...

Chapter 7 slide 37 Other Useful Member Functions Member Function DescriptionExample at(elt) Returns the value of the element at position elt in the vector cout << vec1.at(i); capacity() Returns the maximum number of elements a vector can store without allocating more memory maxelts = vec1.capacity(); reverse() Reverse the order of the elements in a vector vec1.reverse(); resize (elts,val) Add elements to a vector, optionally initializes them vec1.resize(5,0); swap(vec2) Exchange the contents of two vectors vec1.swap(vec2);

Copyright 2003 Scott/Jones Publishing Standard Version of Starting Out with C++, 4th Edition Chapter 7 Arrays